Suspension tuning can be a controversial topic among automotive enthusiasts. Debates often rage over the advantages and disadvantages of different spring rates, damper valving, coilover kits, strut bars, rollcages, etc.
If you've done your research and tested different suspensions, you'll recognize what to strive for and which products work best for you. Each suspension is different for road course, autocross, street and show applications. For Project Silverstone, we strived to obtain the best possible balance for a mostly street driven car. As a result, the '03 GTI was outfitted several years ago with H&R coilovers at Evolution Sports in Kirkland, WA. The coilovers feature a threaded strut body with vehicle-specific damper valving and progressive springs, enabling the car to be safely lowered between 1.8-2.5" below factory height. Our GTI was set approximately 2" lower, providing a stiffer and aggressive handling experience as well as enhancing its visual appeal on 19" BBS LM wheels.
Lowering problemsUnfortunately, lowering our GTI triggered some problems that we had originally overlooked. Let's recollect VW's use of the McPherson strut front suspension. The design is optimum at factory ride height because the control arms - the components connecting the steering knuckles to the chassis - are level, creating a geometrical suspension.
Once the car was lowered, the geometry was upset, affecting the suspension in four ways: 1. camber, 2. toe angle, 3. roll center, 4. control arm bushings.
Camber refers to the angle at which the wheels sit vertically on the pavement when looking from the front or rear of the car. As a wheel moves up and down, especially during cornering, the camber changes. In an ideal camber curve, the top of the tire tilts inward while the bottom of the tire tilts outward, allowing more tire to remain on the pavement during cornering. This is called negative camber. Because lowering the car altered the suspension geometry, we lose the optimum camber conditions, causing additional understeer and loss of traction, thus impairing the handling.
Toe angle refers to the orientation of the wheels when viewed from above. Because this is disrupted when a car is lowered, the toe angle will change as the wheels go up and down, causing the tires to steer themselves over bumps; this is also called bumpsteer. In a turn, misaligned toe angle is aggravating to a driver because it confuses whether the car is losing grip or experiencing bumpsteer.
Roll center refers to the force trying to roll the body of a car. When cornering, the front and rear suspension want to roll but are detered by the roll center. It's important to keep the front and rear roll centers correct or the rear suspension can easily be overloaded, forcing it to roll and making the car unstable. Lowering the car upsets the balanced roll center and makes the front of the car feel less connected to the rear, in turn causing more body roll and understeer.
Control arm bushings have a certain range of motion. When we lower a car, the range is effectively used up and the bushings are put in a tighter position, giving less compliance. While the suspension is under load during hard cornering, the bushings can run out of travel and then bind up. When this happens, the bushings can be damaged, and in extreme cases the tires may bounce off the road because the bushings become ineffective.
H2Sport solutionBecause a lowered Mk4's geometry is misaligned by the poorly angled control arms and steering tie rods, H2Sport has developed a solution. It uses different steering knuckles to replace the factory components. H2Sport's Sport Spindle relocates the control arms and steering tie rods back to their optimum positions, and restores the GTI's geometry by lowering the lower ball joint and tie rod mount by 2".
What's more, camber angles are also corrected, providing more grip to the front tires. The toe angle is fixed, eliminating nasty bumpsteer, while the roll center is restored to balance the car and reduce body roll. Finally, the control arm bushings are able to move freely.
The Sport Spindles are supplied as bolt-on, do-it-yourself kits for the Mk4 platform, designed for cars lowered between 1 and 3". Since it takes time and money to remove and reuse the existing wheel bearings and hubs, H2Sport includes new, pre-assembled units with their spindle kits. Additionally, extended sway bar links are also provided. The only reusable piece from the factory spindle is the ABS sensor.
The kits are available in three different stages. We took the car to VW Specialties (see sidebar) who installed the first stage, which includes the pair of spindles and sway bar end links. Stage 2 consists of sport camber mounts to assist with constant negative camber. Stage 3 adds new control arms with spherical bearings. This kit will maintain precise suspension geometry, making the handling more precise and responsive.
Stay tuned for Mk3 and Mk5 spindles that are in production and should be available soon.